Rubber composition and weatherstrip

Abstract

A rubber composition having good specific gravity, rigidity and electrical resistivity is realized. The rubber composition is foamed and has a torsional rigidity of 1.30 MPa or more and a volume resistivity of 1.0 × 10 6 Ω·cm or more.

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a weatherstrip. [Background technology]

[0002] The specific gravity of rubber compositions used in rubber products can be reduced by foaming. For example, there is a demand for lower specific gravity in weather strips attached to automobiles to reduce their weight.

[0003] Foamed rubber compositions tend to have reduced mechanical properties such as rigidity compared to unfoamed rubber compositions. This tendency to decrease generally increases as the foaming amount is increased to reduce the specific gravity. As an example of a material that combines low specific gravity and high rigidity, Patent Document 1 discloses a glass run channel made of a thermoplastic elastomer with an apparent specific gravity of 0.5 to 0.8 and a torsional rigidity of 3.2 to 4.0.

[0004] Furthermore, reinforcing agents such as carbon materials may be added to improve the mechanical performance of rubber compositions. Such reinforcing agents reduce the electrical resistivity of the rubber composition. A rubber composition with low electrical resistivity is undesirable because it can cause corrosion of the steel plate due to electrolytic corrosion when the rubber composition is attached to a steel plate or the like. Patent Document 2 discloses a weatherstrip with a specific gravity of less than 1.30 and a volume resistivity of 1.0E+6 Ω·cm or greater, as an example of a weatherstrip that combines low specific gravity and high electrical resistivity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-088718 [Patent Document 2] International Publication No. 2017 / 169359 Summary of the Invention [Problem to be solved by the invention]

[0006] However, no rubber composition has been known to date that has a low specific gravity due to foaming or the like, yet has good rigidity and electrical resistivity.

[0007] An object of one aspect of the present invention is to provide a rubber composition that is good in specific gravity, rigidity, and electrical resistivity. [Means for solving the problem]

[0008] In order to solve the above problems, a rubber composition according to one aspect of the present invention is foamed, has a torsional rigidity of 1.30 MPa or more, and a volume resistivity of 1.0×10 6 Ω·cm or more. [Effects of the Invention]

[0009] According to one aspect of the present invention, a rubber composition having good specific gravity, rigidity, and electrical resistivity can be realized. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an automobile equipped with a weather strip according to an embodiment; [Figure 2] FIG. 2 is a diagram showing the correlation between torsional rigidity and specific gravity of a rubber composition according to an example. [Figure 3] FIG. 2 is a diagram showing the correlation between torsional rigidity and volume resistivity of a rubber composition according to an example. [Figure 4] FIG. 2 is a diagram showing the correlation between specific gravity and volume resistivity of a rubber composition according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Rubber composition] The rubber composition according to one embodiment of the present invention is foamed, has a torsional rigidity of 1.30 MPa or more, and a volume resistivity of 1.00×10 6In the present specification, the rubber composition according to one embodiment of the present invention may be referred to as the "rubber composition".

[0012] (component) The present rubber composition is a composition containing rubber. In this specification, rubber refers to a polymer having elasticity and is a general term for natural rubber, synthetic rubber, and thermoplastic elastomer (TPE). In addition to these rubbers, the present rubber composition may contain various additive components as needed.

[0013] The natural rubber and synthetic rubber are preferably vulcanized rubber. Examples of TPEs include block copolymers having hard and soft segments, particularly polystyrene-based, olefin-based, polyvinyl chloride-based, polyurethane-based, polyester-based, and polyamide-based TPEs.

[0014] From the viewpoint of improving the elasticity of the rubber composition, the rubber may be an ethylene-propylene-diene terpolymer rubber (EPDM). Also, from the viewpoint of lowering the specific gravity of the rubber composition, saving energy during production, or improving recyclability, the rubber may be a TPE, particularly an olefin-based TPE (TPO).

[0015] From the viewpoint of improving rigidity, the rubber composition preferably contains a reinforcing agent as an additive component, such as a carbon-based filler or a white filler.

[0016] Carbon-based fillers are reinforcing agents containing carbon, and examples thereof include carbon black. The physical properties of such carbon-based fillers may vary depending on their particle size. The smaller the particle size of the carbon-based filler, the more likely it is to improve rigidity, but the electrical resistivity also tends to decrease. Therefore, when using a carbon-based filler, it is preferable to use multiple types of carbon-based fillers with different particle sizes to appropriately adjust the rigidity and electrical resistivity.

[0017] The carbonaceous filler having a small particle size may have an average particle size of, for example, 50 nm or less, or 45 nm or less. When two or more types of carbonaceous fillers are used, it is preferable to use a carbonaceous filler having such a small average particle size in combination with another carbonaceous filler.

[0018] Examples of white fillers include calcium carbonate, silicon oxide, talc, and clay. The rubber composition may contain one or more of these white fillers. Such white fillers have high electrical resistivity, making it easy to improve the electrical resistivity of the rubber composition. However, the more the amount of white filler added, the more difficult it may be to knead the rubber composition. Furthermore, white fillers generally have a higher specific gravity than carbon-based fillers. From the viewpoints of the specific gravity, rigidity, electrical resistivity, and manufacturability of the rubber composition, it is preferable that the rubber composition contain both a carbon-based filler and a white filler as reinforcing agents.

[0019] When the rubber composition contains a reinforcing agent, it is preferable to reduce the content of the reinforcing agent as much as possible while ensuring the desired rigidity, from the viewpoint of achieving both high rigidity and high electrical resistivity. In other words, it is preferable to reduce the content of the reinforcing agent in the rubber composition to increase the rubber content in the entire rubber composition.

[0020] In the present rubber composition, the content of the reinforcing agent may be 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 100 parts by weight or less, and even more preferably 80 parts by weight or less, based on 100 parts by weight of the rubber content. The content of the reinforcing agent may be 50 parts by weight or more. When the reinforcing agent contains both a carbonaceous filler and a white filler, the proportions of these in the reinforcing agent may be adjusted appropriately.

[0021] The rubber composition may contain other additive components such as microcapsules such as thermally expandable microcapsules, surfactants, vulcanizing agents, vulcanization accelerators, processing aids, process oils, colorants, and dehydrating agents.

[0022] Examples of vulcanizing agents include sulfur, peroxides, resins, amines, and polyols. Among them, when using rubber having a double bond in the main chain or side chain of the polymer, sulfur is preferred as the crosslinking agent.

[0023] (Structure and Properties) The rubber composition is in a foamed state. In other words, the rubber composition is sponge-like. The foamed state of the rubber composition allows the specific gravity to be reduced. The specific gravity of the rubber composition is not particularly limited, but may be, for example, less than 1.00, preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.87 or less. Furthermore, from the viewpoint of achieving both a low specific gravity and high rigidity and high electrical resistivity, the specific gravity of the rubber composition may be 0.70 or more, 0.80 or more, 0.82 or more, more than 0.82, or 0.85 or more.

[0024] The specific gravity of the rubber composition is measured by a method conforming to JIS K6268:1998 using a sample molded from the rubber composition. Specifically, the weight (g) of the sample in air is measured. Then, the weight (g) of the sample immersed in water is measured. The specific gravity is calculated using the following formula (1): Specific gravity = weight in air / weight when immersed in water (1)

[0025] The foamed cells of the present foamed rubber composition may be voids surrounded by microcapsules derived from thermally expandable microcapsules or the like, voids derived from a chemical foaming agent or the like, or other voids.

[0026] This rubber composition has a torsional rigidity of 1.30 MPa or more, achieving both a low specific gravity due to foaming and good mechanical strength. Torsional rigidity is the apparent torsional modulus value at 23±2°C measured using a method in accordance with JIS K6261-3:2017. Torsional rigidity is an index of the ability to resist twisting (torque) applied to an object, and the higher the value, the better the rigidity of the rubber composition.

[0027] The torsional rigidity of the rubber composition is 1.30 MPa or more, preferably 1.35 MPa or more, more preferably 1.40 MPa or more, and even more preferably 1.41 MPa or more. From the viewpoint of achieving high rigidity, low specific gravity, and high electrical resistivity, the torsional rigidity of the rubber composition may be 2.00 MPa or less, 1.80 MPa or less, less than 1.77 MPa, 1.75 MPa or less, 1.70 MPa or less, or 1.69 MPa or less.

[0028] The rubber composition has a volume resistivity of 1.00×10 6 Ω·cm or more. Volume resistivity is an index that indicates the electrical resistance to electricity flowing inside an object, and is calculated as the electrical resistance value per unit volume. The higher the volume resistivity value, the more difficult it is for electricity to flow. Volume resistivity is measured using a method that complies with JIS K6271-1:2015.

[0029] The electrical resistivity of this rubber composition is 1.00 x 10 6 Ω·cm or more, 1.00×10 8 It may be 1.00×10 Ω·cm or more. 10 It may be 1.00×10 Ω·cm or more. 12 It may be 1.00×10 Ω·cm or more. 14 The electrical resistivity of the rubber composition may be 1.00×10 16 It may be Ω·cm or less.

[0030] (Method of manufacturing the rubber composition) The method for producing the rubber composition is not particularly limited, but may include, for example, a step of mixing the rubber and, if necessary, other components, using a kneading machine such as a Banbury mixer, an internal mixer, a kneader, or an open roll mill.

[0031] The method for foaming the rubber composition is not particularly limited, but may be, for example, a method in which a mixture of components containing thermally expandable microcapsules or a chemical foaming agent is heated. The heating is preferably carried out by heating for vulcanization and / or molding of the rubber composition, but heating may also be carried out in other steps.

[0032] One embodiment of the present invention is a molded article of the rubber composition. That is, the molded article according to one embodiment of the present invention is obtained by carrying out a step of vulcanizing the rubber composition and a step of molding the same. Hereinafter, the molded article according to one embodiment of the present invention may be referred to as the "molded article."

[0033] The vulcanization reaction of the rubber composition can be carried out by adding a vulcanizing agent and, if necessary, additives such as a vulcanization accelerator, and then heating the mixture. Heating for vulcanization and molding are preferably carried out simultaneously. The molding method for the molded article is not particularly limited, and may be, for example, an extrusion molding method or a mold molding method.

[0034] The molded article is not particularly limited, but examples thereof include rubber parts for automobiles. Suitable examples of rubber parts for automobiles include weather strips and glass runs. Weather strips may be attached to automobile doors. The rubber composition can also be applied to rubber parts such as gaskets for housing.

[0035] [Weatherstrip] 1 is a side view schematically showing an automobile 100 to which a weatherstrip 102, which is the present molded article, is attached. As shown in FIG. 1, the present molded article may be a weatherstrip 102 attached to a door 101 of the automobile 100. That is, the present rubber composition can be suitably used for the weatherstrip 102 attached to the door 101 of the automobile 100.

[0036] The weatherstrip 102 is a member attached to the periphery of the door 101, and forms a seal between the door 101 and an opening in the automobile 100. The door 101 is a passenger compartment door of the automobile 100, but is not limited to this. The door of the automobile 100 to which the weatherstrip 102 is attached may be, for example, a luggage compartment door, an engine compartment door (also called an engine hood or bonnet), or any other door.

[0037] The weatherstrip 102 may be obtained by extrusion molding the present rubber composition. The weatherstrip 102 may have an extruded portion and a molded portion. In this case, the present rubber composition may be used in at least a portion of either the extruded portion or the molded portion, or may be used in both. In other words, the weatherstrip 102 according to one embodiment of the present invention may have a portion made of the present rubber composition.

[0038] 〔summary〕 The rubber composition according to the first aspect of the present invention is foamed, has a torsional rigidity of 1.30 MPa or more, and a volume resistivity of 1.00×10 6 Ω·cm or more.

[0039] A weatherstrip according to a second aspect of the present invention has a portion made of the rubber composition of the first aspect and is attached to an automobile door.

[0040] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0041] An embodiment of the present invention will now be described.

[0042] (component) The raw rubber was mixed with two types of carbon-based fillers and a white filler as reinforcing agents, thermally expandable microcapsules and a chemical blowing agent as foaming agents, and other additives, and then vulcanized and molded to create a molded rubber composition. Hereinafter, the raw rubber will be referred to as the "polymer," and the two types of carbon-based fillers will be referred to as the "first carbon" and the "second carbon," respectively.

[0043] EPDM was used as the polymer. Carbon black with a particle diameter of 39 to 55 nm (average particle diameter 43 nm) was used as the first carbon, and carbon black with a particle diameter of 49 to 60 nm was used as the second carbon. Calcium carbonate was used as the white filler. Matsumoto Microspheres manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. were used as the thermally expandable microcapsules, and OBSH and ADCA were used as the chemical foaming agents.

[0044] The content of each component was set as shown in Table 1 below, and samples A to H were obtained as molded articles obtained from formulations A to H, respectively. Vulcanization molding was carried out by extrusion molding. The content of each component is shown in parts by weight (phr) relative to 100 parts by weight of polymer. The polymer content in each formulation was the same.

[0045] [Table 1]

[0046] (Evaluation method) The specific gravity, torsional rigidity and volume resistivity of each sample were measured.

[0047] The specific gravity was measured by a method in accordance with JIS K6268:1998 and calculated using the above formula (1). A specific gravity of less than 1.00 was evaluated as good.

[0048] The torsional rigidity was measured by measuring the apparent torsional modulus at 23±2°C using a Gehman torsion tester (TM-501, manufactured by Ueshima Seisakusho Co., Ltd.) according to JIS K6261-3:2017. Specifically, each sample was cut into 3mm x 40mm pieces, and the rigidity was evaluated based on the recovery amount after twisting 180° with a specified wire. A torsional rigidity of 1.30 MPa or higher was considered good.

[0049] The volume resistivity was measured using a digital insulation system (DSM-8104, manufactured by Hioki E.E. Corporation) or a Hiresta (registered trademark) IP (MCP-HT250, manufactured by Mitsubishi Petrochemical Co., Ltd.) according to a method conforming to JIS K6271-1:2015. Specifically, each sample was cut into a 100 mm square sheet, and a voltage of 1 to 100 V was applied to measure the volume resistivity of each sample. The volume resistivity was 1.00 × 10 6 Ω·cm or more (1.00E+6Ω·cm or more) was evaluated as good.

[0050] (result) The evaluation results for each sample are shown in Table 2 below. Figure 2 shows the correlation between the torsional rigidity and specific gravity for each sample. Figure 3 shows the correlation between the torsional rigidity and volume resistivity for each sample. Figure 4 shows the correlation between the specific gravity and volume resistivity for each sample.

[0051] [Table 2]

[0052] As shown in Table 2 and Figures 2 to 4, the specific gravity of all samples was 1.00 or less. In addition, all samples except for sample H had a torsional rigidity of 1.30 MPa or more. In addition, samples F to H had a volume resistivity of 1.00 × 10 6 These results demonstrate that samples F and G are compacts with good specific gravity, torsional rigidity, and volume resistivity. [Industrial Applicability]

[0053] The rubber composition according to one embodiment of the present invention can be used for, for example, weather strips, glass runs, gaskets, and the like. [Explanation of symbols]

[0054] 100 Automobiles 101 Door 102 Weatherstrip

Claims

1. It is foamed, has a torsional rigidity of 1.30 MPa or more, and a volume resistivity of 1.00×10 ６ Ω cm or more and a specific gravity of 0.87 or less, The rubber includes a first carbon and a second carbon having different particle sizes, The rubber is an ethylene-propylene-diene terpolymer rubber (EPDM), The first carbon is carbon black having a particle diameter of 39 to 55 nm, The second carbon is carbon black having a particle diameter of 49 to 60 nm, the content of the first carbon is 12 to 31 parts by weight relative to 100 parts by weight of the rubber, The rubber composition has a content of the second carbon of 45 to 50 parts by weight per 100 parts by weight of the rubber.

2. A weather strip attached to an automobile door, having a portion made of the rubber composition of claim 1.

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